Projectile for mortar



April 16, 1957 H. o. DONNER PROJECTILE FOR MORTAR '2 Sheets-Sheet 1 Filed June 9, 1953 mvzivmk flaws 02W 2012116)" April 16, 1957 H. o. DONNER PROJECTILE FOR MORTAR Filed June 9, 1953 2 Sheets-Sheet 2 INVENTOR. Hans 0220 flanker #5 val/@5111, M4

flGENf-S! PROJECTHJE FOR MORTAR Hans Otto Donner, Tampere, Finland, assignor to Soltam Ltd, Haifa, Israel Application June 9, 1953', Serial No. 360,559

Claims priority, application Finland April, 1953 2 Clfims. (Cl. 102-93) This invention relates. tonew andvery practicable improvementsrin projectiles forinfantry mortars, with a view to increase their-initial velocity and to lengthen their range.

.The infantry mortar is a weapon provided with a smooth-bored barrel for ejecting fin-stabilized projectiles atanangle of elevation usuallyexceeding 30 degrees, with the breech end of the barrel being supported during ejection by means ofa ball or cardan. type joint on a base plate and with the muzzleportion of the barrel attached by means of a springconnectorto a cradle suitably supported by a bipod or tripod.

As mortars are infantry weapons, the general trend is towards making .themortar as light in weight as possibleto facilitate its being transported. This is why high pressures are generally not used at-all for. discharging infantry mortars. Should itlbe desirable to lengthen the rangeof the mortar, i. e. to increase the initial velocity of the projectile while using mortars and projectiles of known types, it wouldbe necessary toincrease the pressure and, consequently,-make the-barrel thicker with the result that the mortar becomes heavy and difficult to move around in combat.

A primary object of the present inventiou is to produce for existing mortars alight weight projectile that, while allowing a high initial velocity, has a good ballistic co efiicient and thus results in long range and good target accuracy.

The inventionis characterizein-that the projectile is ejected through an unrifled barrel by using a combined thrust and centering device on the projectile. Though the use of projectiles of the thrustdevice type in rifled weapons is already known from projectiles of the hardrnetal core type capable of piercingarmour plates, the application of a thrust and centering device to mortar projectiles provided with a fin .is a novel and similarlyit is also novel touse it in light-weightsmooth-bored mortars of the type described supra.

To illustrate the invention, the following description andthe accompanying annexed drawings refer to some constructions .of mortar projectiles consistent with the present invention, however, without limiting the scope of the invention exclusively to the structures described herein.

On the accompanying drawings;

Fig. 1 shows a mortar projectile, constructed in accordance with the invention and provided with a thrust and centering device, inserted in a mortar barrel and viewed from one side, with the upper part of the'projectile shown in longitudinal section.

Fig. 2 shows the sameprojectile and its retainer device viewed fromthe front end.

Fig. 3 shows a mortar projectile in accordance with a modification of the present invention and provided with.

unfolding fins, with theupper part shown inlongitudinal section the projectile being insertedinto'thebarrel of the mortar.

Fig. 4 shows armortar projectile in. accordance with a further modification of the present invention inserted into Patented Apr. 16, 1957 the barrel of a mortanwith part shown in longitudinal ICE ' section.

The mortar projectile, according to the first form of thepresent inventionzshown' in Figs. 1 and 2 is shown in position in the barrel 1 of a mortar. The projectile comprises a body 3. provided at its front end with a detonatplosiongases from'escapingxbetween the inner'periphery of the barrell and thethrustplate. Thus the body 3 of theprojectile rests against the thrust plate-6 by means of the projecting rear-end 5 and with the fore end of the-projectile againstthefore part of a centering device 9and more particularly against thering surface 8 thereof. In the showing'of Figures '1 and 2, the centering device consists of atube '17 substantially as long as the projectile, the diameter ofits fore:part fitting with a sliding fitinto the barrel l'of the mortar and the diameter of the rearpart beingslightly smaller. At its rear part the centeringdevice is attached by means of threads to the thrust plate 6. in addition, the rear part of the thrust device is;provided with circumferentially extended slots 10 and i1 and extended from the front end up to the slots 10 and 11, a number of longitudinal-extended slots: inthe modification shown'in Figs. 1 and 2, there are four slots 12, 13, Hand 15. The tube like' centering device is divided by the longitudinalislots into foursegments. The fore part of the centering-device isalso provided with a shallow, circumferential groove 16' inwhich there is during transport a belt and a safety wire for preventing the segments from opening. Thisis removed before inserting the projectile into the barrel.

A projectile constructed in accordance with Figs. 1 and 2 is used as follows: The projectile is inserted from the rear into the tube 17 in such a way that the fore end of the projectile body rests against the ring-like inner surface 8 of the tube. The fins of the projectile tail 4 are now freely within'the rear end of the tube.

Then-the thrust-plate dis screwed into the rear end of the centering tube and'into engagement with the projecting rear end 5 of the tail to center'the projectile exactly on the center line of the tube. When firing, the safety ring is first removed from the groove 16 and the projectile'is dropped in the usual way into the mortar barrel. Depending on the lock device used and on the location of the basic charge, firing occurs either when the projectile hits the bottom of the barrel or by means of a firing mechanism at the moment required. Now the'pressure of the powder gaseseifect the rear surface of the thrust plate 6 and the thrust plate thrusts the projectile body by means of the'projecting rear end 5 as well as the centering-device 9 which restsagainst the outer edge of the thrust plate. When the projectile leaves the mortar-barrel, air resistance acts brakingly on the front surface of the centering device 9 and thrusts it backwards whereat the separate segments at the fore edge openoutwards, with theair resistance then turning them all to =thesides and theybreak off completely of the thrust plate is-considerablylarger than the maximum diameter of the projectile, but the weight of the thrust and centering device is small, the projectile receives, when normal barrel pressure is being used, a correspon'dingly higher initial'velocity and also a' longer range. Due to it being possible to make the diameter of the fin group larger than the maximum diameter of the body of the projectile and also to decrease the resistance of the fin group considerably by making the fins very thin, the stability of the projectile can be made good. This is entirely possible on account of the pressure of the basic charge powder gas not being able to aifect in any way the fin group at'the firing moment.

The modification of Fig. 3 shows a mortar projectile consistent with this invention and having unfolding fins and separate centering components at the fore end of the projectile. The reference numeral 1 designates the 'muzzle part of a mortar barrel 1, 2' the fuse of the mortar projectile and 3 the body of the projectile, 4 the tail tube with fins 6' capable of pivoting outward around pins 5. A centering ring 7' of light metal encircles the rear end of the projectile and rests against the rear surface of the body and at the same time func tioning as thrust component. In addition, the fore end of the projectile is provided with slightly rearward slanting borings 8 in end of which a spiral spring and a pin 9 are inserted. When in stock, the pin in the projcctile is provided with a safety ring that prevents the springs from pressing the pins 9 out of the borings 8'.

Charging and discharging of the mortar with these projectiles is accomplished as follows: The projectile is inserted into the barrel of the mortar in the usual way. The outer surface of the centering ring 7' now guides the rear part of the projectile, and when the projectile has entered the barrel up to the point shown on Fig. 3 the safety ring 10 remains on the muzzle of the barrel while the projectile continues its course in the barrel. When the safety ring has come off, the pins 9 center the fore end of the projectile on the center line of the barrel. As the mortar is fired the powder gases thrust both the centering rings 7 and the projectile forward. As the projectile leaves the muzzle of the barrel the springs push the centering pins 9' completely out of the borings S and the resistance of air retards the ring 7 so that it is left behind and the fins 6 unfold. The tin-stabilized projectile now continues its flight alone.

In the modification of Fig. 4 the mortar projectile is provided with a basic charge tube and fixed fins as well as with a centering device and a thrust plate, mortar with the upper part of the projectile shown in longitudinal section up to the centre line. The numeral la indicates the mortar barrel in longitudinal section, the numeral 2a indicates the fuse of the projectile, the numeral 4a the basic charge tube with its radially located borings, the numeral 5a the tail with its fixed fins. The tail and rear end of the projectile is encircled by a ring-like part 6a the fore part of which forms the thrust plate 7a bearing on the internal surface of the barrel 1a. The inside of the ring-like part 6a is provided with the grooves 8a in which the fins are capable of moving in the longitudinal direction of the barrel. The front edge of the ring-like part 6a and so also the inner edge of the thrust plate 7:: are supported along the ring-like surface 9a against the body of the projectile.

The fore part of the projectile is provided with slots 10a parallel to the longitudinal axis, and towards the rear end of each slot there is a pin 11a. On each pin Illa there is hinged a movable centering lug 12a which is fitted with a spiral spring in such a way that if the external end of centering device is released from the position shown in the figure, the device turns forward to the position 12 indicated by dash-lines.

The device described herein functions, when firing, as follows: When the projectile is inserted into the barrel and firing occurs, the powder gases thrust the ring-like 'part 611, made of light metal, and its thrust plate 7a,

movable from the projectile body after leaving the barrel by the pressure of the air acting thereagainst, said tube forward with greater speed than with which the gases thrust the heavier body-part of the projectile. At this stage the contact of the surface 9a becomes absolutely tight and the whole projectile is set into motion at an ever increasing velocity. The centering lugs 12a center the fore part of the projectile on the center line of the barrel. As the projectile leaves the barrel, the centering lugs 12a are turned forward and in spite of air resistance are folded into the slots 10a thus making the tip of the projectile completely streamlined. Simultaneously the resistance of air frees the thrust plate 7a from the projectile body and the plate is left behind as the fins of the projectile tail move forwards along the grooves 8a of the tube-like part. The projectile now continues its flight alone.

As seen from what is stated above, the invention comprises a number of various applications for centering a mortar projectile in the barrel and at the same time, by using a thrust plate, very high initial velocities and long ranges with good target accuracy are obtainable with constructions consistent with the invention.

Of course, a motor projectile with thrust plate and centering device and consistent with the invention can also otherwise be produced within the limits of the invention. The projectiles described above are only some structural principles. In the above description it has been stated that the centering device or devices fall apart under the effect of air resistance or spring force. Of course, it is also possible to design constructions in which the residual gases compressed in the centering device at the moment of discharge open or disassemble the centering device by means of the expansion of the residual powder gases as the projectile leaves the mortar barrel. Projectiles provided with a centering and thrust device similar to and consistent with the invention are capable of initial velocities of 400 to 500 metres per second and, correspondingly ranges exceeding 20,0000 metres when used in standard weapons having a calibre of 4 to 8 inches.

Having described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. A fin-stabilized under-caliber projectile for discharge from a smooth-bored mortar barrel, comprising an elongated forwardly and rearwardly tapering body having radially extended fins at its rear end, and a centering tube enclosing at least the rear end portion and fins of said body, said centering tube having a rearwardly facing thrust surface to be exposed to the explosive pressures in the barrel for propelling the projectile body and centering tube out of the barrel and being rearwardly reenclosing said body from its rear end to a point slightly rearward of the point of greatest diameter on said body, said fins being pivotally mounted within slots defined in the rear end portion of the body and held in collapsed position within said slots by said tube, the forward part of said tube being formed with rearwardly inclined, ra-

ially extended borings, and spring pressed centering pins mounted in said borings to engage the barrel during the presence of the projectile within the latter and then to be ejected from said borings when the projectile leaves the barrel.

2. A fin-stabilized under-caliber projectile for discharge from a smooth-bored mortar barrel, comprising an elongated forwardly and rearwardly tapering body having radially extended fins at its rear end, and a centering tube enclosing at least the rear end portion and fins of said body, said centering tube having a rearwardly facing thrust surface to be. exposed to the explosive pressures in the barrel for propelling the projectile body and centering tube out of the barrel and being rearwardly removable from the projectile body after leaving the barrel by the pressure of the air acting thereagainst, said tube enclosing said body from its rear end to a point slightly rearward of the point of greatest diameter on said body, said tube having an external diameter throughout most of its length which is smaller than the internal diameter of the barrel and having a front end portion enlarged to the 5 internal diameter of said barrel to provide said thrust surface, said body having radially opening slots forward of said tube, and centering lugs pivotally mounted in said slots and resiliently urged to inoperative position within said slots upon discharge of said projectile from the barrel. 10

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS France Aug. 20, Denmark Mar. 15, 

